Method of and apparatus for identifying a signal transmitting source

ABSTRACT

A method of and apparatus for identifying a signal transmitting source detects a switching of a signal on the reception side thereby to prevent a transmission error from occurring when a signal is switched. The apparatus for identifying a signal transmitting source comprises a transmitting source identifying code extracting circuit for extracting a transmitting source identifying code provided in a SDDI format header of a received signal, a preceding transmitting source identifying code holding circuit for detecting a change of the transmitting source identifying code, and a transmitting source identifying code comparing circuit for detecting a switching of a transmitted signal based on the transmitting source identifying code thus changed, thereby detecting a switching of the transmitting source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.08/618,998, filed Mar. 21, 1996 now U.S. Pat. No. 6,188,438.

BACKGROUND OF THE INVENTION

The SMPTE 259M has hitherto been known as the standard for serialdigital interface (hereinafter simply referred to as a “SDI”) of videosignal used in professional and broadcasting station video equipments.This SMPTE 259M standard describes a serial digital interface for 525/60and 625/50 digital television equipment operating with either 4:2:2component signals or 4f_(sc) composite digital signals.

FIG. 1 of the accompanying drawings shows the SDI format.

As shown in FIG. 1, the SDI format comprises an EAV (end of activevideo) 131 provided at the starting portion, an ancillary signal area132 provided next to the EAV 131, and a SAV (start of active video) 133provided next to the ancillary signal area 132. The EAV 131 and SAV 133comprise words (3FF, 000, 000, XYZ)_(h) each word of which is ahexadecimal signal. The EAV 131, the ancillary signal area 132, and theSAV 133 are composed of 276 words for the 525/60 television receiver,and composed of 288 words for the 625/50 the television receiver.

The SDI format further includes an effective image signal area 134provided next to the SAV 133, and the effective image signal area 134 isused to transmit an image signal. The effective image signal area 134 isfollowed by a timing reference signal EAV 135. The image signalcomprises a luminance signal Y and blue and red color difference signalsCb, Cr each of which is a 10-bit digitized signal, and the luminancesignal Y and the blue and red color difference signals are arranged inthe sequential order of Cb, Y, Cr and Y. The effective image signal area134 is composed of 1440 words for both the 525/60 television receiverand the 625/50 television receiver. Therefore, an area which resultsfrom adding the effective image signal area 134 to the EAV 131, theancillary signal area 132 and the SAV 133 is composed of 1716 words forthe 525/60 television receiver, and composed of 1728 words for the625/50 television receiver.

The effective image signal area 134 is followed by the timing referencesignal EAV 135. The timing reference signal EAV 135 is composed of words(3FF, 000, 000, XYZ)_(h) each word of which is a hexadecimal signal. TheSAV 133, and the EAV 131, 135 are inserted into the horizontal blankingperiod.

A parallel signal according to the SDI format is converted in the formof parallel to serial signal, and in this case, the LSB (leastsignificant bit) of any data word shall be transmitted first. Then, theserial signal is converted into a scrambled NRZI (nonreturn-to-zeroinverted) signal, channel-coded, and thereby transmitted as serialdigital video signal of 270 Mbit/sec.

In the SDI format signal transmission system, the serial digital videosignal is transmitted with a word synchronization of word unit. However,in this SDI format signal transmission system, it is frequently demandedthat a plurality of signals are switched by a signal switching device.This signal switching device switches and outputs the inputted signal inthe form of the serial signal. Before or after the signal is switched bythe signal switching device, a word synchronization of signal becomesdiscontinuous, and a synchronization of switched signal is not achieved,thereby causing a transmission error. The transmission errorcontinuously occurs until a word synchronization of signal isestablished by the next EAV.

For this reason, according to the SDI format, a signal is switchedduring a vertical blanking period, whereby a signal error that occurreddue to a discontinuous word synchronization of signal generated when thesignal is switched can be prevented from becoming conspicuous on apicture screen of a television receiver on the reception side.

As described above, in the SDI format signal transmission system, beforeor after a plurality of signals are switched by the signal switchingdevice, a word synchronization of signal becomes discontinuous, and asynchronization of switched signal cannot be established, resulting in atransmission error. In order to avoid the occurrence of transmissionerror, a signal has to be switched during the vertical blanking period.

SUMMARY OF THE INVENTION

In view of the aforesaid aspect, it is an object of the presentinvention to provide method of and apparatus for identifying a signaltransmitting source in which the reception side detects a switching of asignal thereby to prevent a transmission error from occurring whensignals are switched.

According to an aspect of the present invention, there is provided areceiving apparatus for receiving a transmitted signal with atransmitting source identifying code added thereto at a transmission endof a transmission line as a received signal. This receiving apparatuscomprises transmitting source identifying code extracting means forextracting the transmitting source identifying code from the receivedsignal, transmitting source identifying code change detecting means fordetecting a change of the transmitting source identifying code extractedfrom the received signal by the transmitting source identifying codeextracting means, and transmitted signal switching detecting means fordetecting a switching of the transmitted signal based on thetransmitting source identifying code whose change was detected by thetransmitting source identifying code detecting means.

According to another aspect of the present invention, there is provideda method of switching a transmitted signal which is comprised of thesteps of adding a transmitting source identifying code to a transmittedsignal at a transmitting end of a transmission line, extracting thetransmitting source identifying code at a receiving end of thetransmission line, detecting a change of the transmitting sourceidentifying code extracted at the receiving end, and detecting aswitching of the transmitted signal based on the transmitting sourceidentifying code this changed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a SDI format;

FIG. 2 is a diagram showing a SDDI format;

FIG. 3 is a diagram showing a header area in the SDDI format shown inFIG. 2 more fully;

FIG. 4 is a block diagram showing a video signal output portion in aSDDI format video equipment;

FIG. 5 is a block diagram showing a header processor shown in FIG. 4more in detail;

FIG. 6 is a circuit diagram of a header detector shown in FIG. 5;

FIG. 7 is a circuit diagram showing more fully a transmitting sourceidentifying code comparing circuit shown in FIG. 5;

FIGS. 8A through 8F are timing charts showing a manner in which aswitching of a signal is detected at the line unit according to thepresent invention;

FIG. 9 is a block diagram showing a header processor for detecting amanner in which a switching of a signal is detected at the field unitaccording to another embodiment of the present invention;

FIG. 10 is a circuit diagram showing a line-masking circuit shown inFIG. 9 more in detail; and

FIGS. 11A through 11I are timing charts showing a manner in which aswitching of a signal is detected at the field unit according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to thedrawings.

FIG. 2 shows a SDDI (serial digital data interface) format, and thisSDDI format has been independently developed by the same assignee ofthis application. In comparison with the SDI (serial digital interface)format shown in FIG. 1, the SDDI format can transmit not only digitaldata in the effective image signal area but also compressed and encodedimage information or audio information or control information togetherwith original image information.

As shown in FIG. 2, the SDDI format comprises an EVA 80 (end of activevideo), an ancillary signal area 81 provided next to the EAV 80, and aSAV (start of active video) 82 provided next to the ancillary signalarea 81. The EAV 80 and the SAV 82 are composed of words (3FF, 000, 000,XYZ)_(h) each word of which is a hexadecimal signal. The EAV 80, theancillary signal area 81 and the SAV 82 are composed of 276 for the525/60 television receiver, and 288 words for the 625/50 televisionreceiver.

The SAV 82 is followed by a payload area 84, and the payload area 84contains a compressed image signal therein. This compressed image signalis digital data which results from high-efficiency-coding a videosignal. The payload area 84 is followed by CRCC (cyclic redundancy checkcode) 0, CRCC1 86.

The CRCC0, CRCC1 will be described below. An information frame, which istransmitted through a communication network, is added with a remainderterm which results from a certain division, and then transmitted. Atransmission error is checked by comparing a remainder term, whichresults from effecting a similar calculation on a received signal on thereceiving end, with the remainder term transmitted thereto. Generatorpolynomial is used in such division.

The payload area 84 and the CRCC0, CRCC1 86 are composed of 1440 wordsfor both the 525/60 television receiver and the 625/50 televisionreceiver.

Accordingly, an area which results from adding the payload area 84 andthe CRCC0, CRCC1 86 to the EAV 80, the ancillary signal area 81 and theSAV 82 is composed of 1716 words for the 525/60 television receiver, andcomposed of 1728 words for the 625/50 television receiver.

In particular, according to this embodiment, the ancillary signal area81 includes a header area 83 provided at its beginning. The header area83 includes a transmitting source identifying address, and is composedof 53 words.

The payload area 84 is followed by a timing reference signal area EVA,and the EVA 85 is composed of words (3FF, 000, 000, XYZ)_(h) each wordof which is a hexadecimal signal. The SAV 82, the EAV 80 and the EAV 85are inserted into the horizontal blanking period.

FIG. 3 is a diagram showing a header area 83 in the SDDI format more indetail. As shown in FIG. 3, an ADF (ancillary data flag) 90 provided atthe beginning of the header area 83 is composed of 3 words (000, 3FF,3FF)_(h) each word of which is a hexadecimal signal. The ADF 90 is acode indicative of the beginning of the ancillary signal packet. A dataID 91 indicates contents of ancillary signal, such as digital audiodata, time code or error-detection code.

A block number 92 is used to detect a continuity of data packet, and candetect a continuity of data packets ranging from 0 to 255 by effecting8-bit count-up. A data count 93 is used to count the number of words ofuser data in the ancillary signal.

Line number 0 and line number 1, generally denoted by reference numeral94, are used to indicate the number of scanning lines from 1 to 525.

CRCC0 and CRCC1, generally denoted by reference numeral 95, areerror-detection codes used to detect errors in the areas ranging fromADF 90 to the line number 0 and line number 1, 94.

A destination address 96 is used to indicate address of datadestination, and a source address 97 is a transmitting sourceidentifying code used to indicate a data transmitting source. The sourceaddress 97 adds unique individual codes to video equipments when thesevideo equipments are delivered. In this embodiment, the source address97 is composed of 16-word data area which comprises 128-bit data.

A block type 98 is used to indicate a block type of the payload area 84.A CRC flag 99 is used to indicate whether or not the CRCC0 and CRCC1, 86provided at the rear end of the payload area 84 are valid. A data startposition 100 is used to indicate a data start position of the payloadarea 84. Reserve 0, reserve 1, reserve 2 and reserve 3, generallydenoted by reference numeral 101, are preliminary ones.

CRCC0 and CRCC1, generally denoted by reference numeral 102, areerror-detecting codes used to detect errors in the areas ranging fromthe destination address 96, the source address 97, the block type 98,the CRC flag 99, the data start position 100, the reserve 0, the reserve1, the reserve 2 and the reserve 1, 101. A checksum 103 is used todetect transfer errors from a sum total of respective digits of datafrom data ID 91 to the CRCC0 and CRCC1, 102.

FIG. 4 shows, in block form, a video signal output portion of a SDDIformat video equipment.

As shown in FIG. 4, a serial signal transmitted through a transmissioncable from a transmission side (not shown) is supplied to a BNC coaxconnector 110. The received serial signal supplied to the BNC coaxconnector 110 is supplied to a serial-to-parallel (serial/parallel)converter 111.

The serial-to-parallel converter 111 waveform-equalizes the receivedserial signal transmitted thereto at 270 [Mbp/s], reproduces a serialclock, and decodes a channel code by scrambled NRZI. Further, theserial-to-parallel converter 111 reproduces a word synchronizing signalby detecting a timing reference signal (EAV/SAV), and converts thereceived serial signal into a 10-bit parallel signal 117.

One 10-bit parallel signal 117 is supplied to an image informationdecoder 113, an audio information decoder 114, and a control informationreceiver 115. The image information decoder 113 extracts a compressedand encoded image signal from the 10-bit parallel signal, and outputs areproduced image signal 119 by decoding this image signal. The audioinformation decoder 114 extracts a compressed and encoded audio signalfrom the 10-bit parallel signal 117, and outputs a reproduced audiosignal 120 by decoding this audio signal. The control informationreceiver 115 extracts control information from the 10-bit parallelsignal 117, and outputs a control signal 130 based on the extractedcontrol information.

The other 10-bit parallel signal 117 is supplied to a header processor112, and the header processor 112 processes signals in the header area83 of the SDDI format. When the header processor 112 processes thesignals in the header area 83, the header processor 112 outputs avariety of signals, such as the transmitting source identifying code anda signal switching detecting signal. Signals of the header area 83processed by the header processor 112 are supplied to the imageinformation decoder 113, the audio information decoder 114 and thecontrol information receiver 115.

The signals of the header area 83 processed by the header processor 112are the transmission source identifying code and the signal switchingdetecting signal 118. The transmitting source identifying code is thesource address 97 shown in FIG. 3.

Arrangement and operation of the header processor 112 shown in FIG. 4will be described in detail below with reference to FIG. 5 to FIGS. 11Athrough 11I.

FIG. 5 is a block diagram showing the header processor 112 for detectingthe switching of signal at the line unit. In this embodiment, thetransmitting source identifying signal which indicates the transmittingsource of the header area 83 added to the SDDI format transmissionsignal is detected by the reception side at the line unit, and theheader processor 112 detects the switching of the transmitting sourcebased on the change of the transmitting source identifying code.

As shown in FIG. 5, a 10-bit parallel signal 6 is a signal which issupplied from the serial/parallel converter 111 shown in FIG. 4 to theheader processor 112. One 10-bit parallel signal 6 is supplied to aheader detector 1. The header detector 1 detects (000, 3FF, 3FF, 140,101)_(h) of a hexadecimal signal of a fixed pattern indicative of thebeginning of the header area 83 of the SDDI format, and supplies aheader detected pulse 7 to a timing generator 2.

FIG. 6 is a circuit diagram of the header detector 1 according to thepresent invention. As shown in FIG. 6, when (0000000000)₂ of a binarysignal, i.e., (000)_(h) of a hexadecimal signal is supplied throughinverters 30-1, 30-2, 30-3, 30-4, 30-5, 30-6, 30-7, 30-8, 30-9, 30-10 toa 10-bit input AND circuit 30 of the first stage, a detected signal issupplied through five flip-flops (FFs) 30-11, 30-12, 30-13, 30-14, 30-15to a 5-input AND circuit 34.

When (1111111111)₂ of a binary signal, i.e., (3FF)_(h) of a hexadecimalsignal is supplied to a 10-bit input AND circuit 31 of the second stage,a detected signal is supplied through three flip-flops 31-1, 31-2, 31-3and four flip-flops 31-1, 31-2, 31-3, 31-4 to the 5-input AND circuit34.

When (0101000000)₂ of a binary signal i.e., (140)_(h) of a hexadecimalsignal is supplied through inverters 32-1, 32-2, 32-3, 32-4, 32-5, 32-6,32-7, 32-8 to a 10-bit input AND circuit 32 of the third stage, adetected signal is supplied through two flip-flops 32-9, 32-10 to the5-input AND circuit 34.

When (0100000001)₂ of a binary signal, i.e., (101)_(h) of a hexadecimalsignal is supplied through inverters 33-1, 33-2, 33-3, 33-4, 33-5, 33-6,33-7, 33-8 to a 10-bit input AND circuit 33 of the four stage, adetected signal is supplied through a flip-flop 33-9 to the 5-input ANDcircuit 34.

When (000, 3FF, 3FF, 140, 101)_(h) of the hexadecimal signal which is afixed pattern indicative of the beginning of the header of the SDDIformat is supplied to the 5-input AND circuit 34, the 5-input ANDcircuit 34 outputs a header detected signal 7.

Referring back to FIG. 5, the header detected pulse 7 from the headerdetector 1 is supplied to the timing generator 2. The timing generator 2is composed of a counter, and the timing generator 2 generates a timingpulse for latching therein the transmitting source identifying codelatch pulse and a variety of information provided within the header ofthe SDDI format when the counter thereof counts the header detectedpulse 7.

The other 10-bit parallel signal 6 is supplied to the transmittingsource identifying code extracting circuit 3, and the transmittingsource code latch pulse 8 is supplied to the transmitting sourceidentifying code extracting circuit 3. The transmitting source codeextracting circuit 3 is composed of a latch, for example. Thetransmitting source code extracting circuit 3 latches therein the dataof the 10-bit parallel signal 6 supplied thereto in response to thetransmitting source identifying code latch pulse 8 supplied thereto as aclock. Thus, the transmitting source identifying code extracting circuit3 latches the transmitting source identifying code 9 therein.

The transmitting source identifying code 9 thus latched is supplied tothe video equipment body (not shown), and thereby used in discriminatingor displaying a signal transmitting source equipment. The transmittingsource identifying code 9 is supplied to a preceding transmitting sourceidentifying code holding circuit 4, and a transmitting sourceidentifying code comparator 5. The preceding transmitting sourceidentifying code holding circuit 4 is composed of a latch, for example.The preceding transmitting source identifying code holding circuit 4latches therein a one-line-preceding transmitting source identifyingcode 10, that has been latched in the transmitting source identifyingcode extracting circuit 3, in response to the transmitting sourceidentifying code latch pulse 8 supplied thereto as a clock. Thepreceding transmitting source identifying code holding circuit 4comprises a transmitting source identifying code change detecting means.

The transmitting source identifying code comparator 5 compares theone-line-preceding transmitting source identifying code 10 latched bythe transmitting source identifying code extracting circuit 3 and thetransmitting source identifying code 3 newly latched by the transmittingsource identifying code extracting circuit 3.

FIG. 7 is a circuit diagram showing more in detail the transmittingsource identifying code comparator 5 shown in FIG. 5.

As shown in FIG. 7, 16-word (128-bit) transmitting source identifyingcode 9 and the preceding transmitting source identifying code 10 aresupplied to 128 exclusive-OR circuits 40-1, 40-2, 40-3, . . . 40-128,respectively. Outputs from the 128 exclusive-OR circuits 40-1, 40-2,40-3, . . . 40-128 are supplied to a 128-input OR circuit 40.

Therefore, when the transmitting source identifying code 9 and thepreceding transmitting source identifying code 10 are not agreed witheach other, the transmitting source identifying code comparator 5determines that the signal is switched, and outputs a signal switchingdetection signal 11.

FIGS. 8A through 8F are timing charts showing a manner in which aswitching of signal is detected at the line unit according to thepresent invention. FIG. 8A shows the 10-bit parallel signal 6, FIG. 8Bshows the header detection pulse 7, FIG. 8C shows the transmittingsource identifying code latch pulse 8, FIG. 8D shows the transmittingsource identifying code 9, FIG. 8E shows the preceding transmittingsource identifying code 10, and FIG. 8F shows the signal switchingdetection signal 11, respectively. A manner in which the switching ofsignal is detected will be described below.

As shown in FIG. 8A, the 10-bit parallel signal 6 is switched from asignal #1 to a signal #2 at a signal switching portion 61. A portionshown hatched in the 10-bit parallel signal 6 represents a header 60 ofSDDI format, and the header 60 is transmitted at every line. The 10-bitparallel signal 6 is supplied to the header detector 1 and thetransmitting source identifying code extracting circuit 3 as shown inFIG. 5.

As shown in FIG. 8B, the header detection pulse 7 is obtained bydetecting the header 60 of the SDDI format. The header detection pulse 7is a pulse with a predetermined pulse width and whose leading edge iscoincident with the leading edge of the header 60 of the SDDI format.The header detection pulse 7 is outputted from the header detector 1 asshown in FIG. 5.

As shown in FIG. 8C, the transmitting source identifying code latchpulse 8 is obtained based on the header detection pulse 7 after apredetermined period elapsed from the header detection pulse 7. Thetransmitting source identifying code latch pulse 8 is outputted from thetiming generator 2 when the timing generator 2 counts the headerdetection pulse 7 as shown in FIG. 5.

As shown in FIG. 8D, the transmitting source identifying code 9 ofaddress #2 is obtained at the trailing edge of the transmitting sourceidentifying code latch pulse 8 that was first detected after the signalhas been switched at the signal switching portion 61. The addresses #1and #2 are addresses of the signals #1 and #2 corresponding to thetransmitting sources.

As shown in FIG. 8E, there is obtained the one-line-precedingtransmitting source identifying code 10 of the transmitting sourceidentifying code. As shown in FIG. 5, the one-line-precedingtransmitting source identifying code 10 is generated from the precedingtransmitting source identifying code holding circuit 4 when thepreceding transmitting source identifying code holding circuit 4 latchestherein the transmitting source identifying code in response to thetransmitting source code latch pulse 8 supplied thereto as a clock.

As shown in FIG. 8F, the signal switching detection signal 11 isobtained at a timing corresponding to the trailing edge of thetransmitting source identifying code latch pulse 8 that was firstdetected after the signal has been switched at the signal switchingportion 61. The signal switching detection signal 11 has a predeterminedwidth of a period corresponding to a difference between the period ofthe transmitting source identifying code 9 and the period of thepreceding transmitting source identifying code 10. As shown in FIG. 5,the transmitting source identifying code comparator 5 generates thesignal switching detection signal 11 by comparing the transmittingsource identifying code 9 and the preceding transmitting sourceidentifying code 10.

According to the above embodiment, the transmitting source identifyingcode is extracted from the SDDI format header of the received signal,the transmitting source code that was added to the transmission signalupon transmission is extracted, the change of the transmitting sourceidentifying code is detected, the change of the transmitting sourceidentifying code indicative of the transmitting source added to thetransmission signal upon transmission is detected, and the switching ofthe changed transmitting source identifying code is detected on thebasis of the changed transmitting source identifying code, whereby theswitching of the transmitting source can be detected at the line unit.

FIG. 9 is a block diagram showing the header processor 112 (shown inFIG. 4) which detects the switching of signal at the field unitaccording to another embodiment of the present invention. In thisembodiment, the receiving side detects the transmitting sourceidentifying code indicative of the transmitting source in the headerarea added to the SDDI format transmission signal at the field unit, anddetects that the switching of the transmitting source when the change ofthe transmitting source identifying code is detected.

According to the SDDI format, line No. 6 or line No. 9 is previouslydetermined as a signal switching position for the 625/50 televisionreceiver, and line No. 10 or line No. 273 is previously determined as asignal switching position for the 525/60 television receiver. Therefore,the transmitting source identifying codes are compared with each otherat the position immediately after the above signal switching position.

In FIG. 9, elements and parts identical to those of FIG. 5 are markedwith the same reference numerals, and therefore need not be described indetail. Thus, only different elements and parts will be described indetail below.

As shown in FIG. 9, the 10-bit parallel signal 6 is supplied from theserial/parallel converter 11 shown in FIG. 4 to the header processor 12.The 10-bit parallel signal 6 is supplied to the header detector 1. Theheader detector 1 detects (000, 3FF, 3FF, 140, 101)_(h) of hexadecimalsignal which is a fixed pattern indicating the beginning of the headerof the SDDI format, and supplies the header detection pulse 7 to thetiming generator 2.

The header detection pulse 7 generated from the header detector 1 issupplied to the timing generator 2. The timing generator 2 is composedof a counter, for example. When the counter of the timing generator 2counts the header detection pulse 7, the timing generator 2 generatestiming pulses for latching a variety of information provided in theheader of the SDDI format, such as a latch number latch pulse 22 and atransmitting source identifying code timing pulse 23.

The timing generator 2 supplies the line number latch pulse 22 to a linenumber extracting circuit 20. The 10-bit parallel signal 6 is alsosupplied to the line number extracting circuit 20. The line numberextracting circuit 20 latches the 10-bit parallel signal 6 therein inresponse to the latch number latch pulse 22 supplied thereto as a clock,whereby the line number extracting circuit 20 latches a line numbersignal 24 therein. The line number extracting circuit 20 is composed ofa latch, for example.

The timing generator 2 supplies the transmitting source identifying codetiming pulse 23 to a line-masking circuit 21. The line number extractingcircuit 20 supplies the line number signal 24 to the line-maskingcircuit 21.

FIG. 10 is a circuit diagram showing more in detail the line-maskingcircuit 21 shown in FIG. 9.

As shown in FIG. 10, when (0100010011)₂ of binary signal, i.e., (275)₁₀of decimal signal is supplied to a 10-bit AND circuit 50 of a firststage through inverters 50-1, 50-2, 50-3, 50-4, 50-5, 50-6, the first10-bit input AND circuit 50 supplies a detection signal to an OR circuit52.

When (0000001100)₂ of binary signal, i.e., (012)₁₀ of decimal signal issupplied to a 10-bit input AND circuit 51 of a second stage throughinverters 51-1, 51-2, 51-3, 51-4, 51-5, 51-6, 51-7, 51-8, the 10-bit ANDcircuit 51 supplies a detection signal to the OR circuit 52. When anyone of the detection signals from the 10-bit AND circuits 50 and 51 issupplied to the OR circuit 52, the OR circuit 52 supplies a detectionsignal to an AND circuit 53. When the detection signal from the ORcircuit 52 and the transmitting source identifying code timing pulse 23are both supplied to the AND circuit 53, the AND circuit 53 outputs atransmitting source identifying code latch pulse 25.

Thus, only when the line number is the next line next to thepreviously-determined signal switching position, i.e., line number 12 orline number 275, the line-masking circuit 21 passes the transmittingsource identifying code timing pulse 23 therethrough, and outputs thesame as the transmitting source identifying code latch pulse 25.

Referring back to FIG. 9, the transmitting source identifying code latchpulse 25 is supplied to the transmitting source identifying codeextracting circuit 3 and the preceding transmitting source identifyingcode holding circuit 4. The other 10-bit parallel signal 6 is suppliedto the transmitting source identifying code extracting circuit 3, andthe transmitting source code latch pulse 25 is supplied to thetransmitting source identifying code extracting circuit 3. Thetransmitting source identifying code extracting circuit 3 is composed ofa latch, for example. The transmitting source identifying codeextracting circuit 3 latches data of the 10-bit parallel signal 6supplied at that time in response to the transmitting source identifyingcode latch pulse 25 as a clock. As a consequence, the transmittingsource identifying code extracting circuit 3 latches therein a 16-word(128-bit) transmitting source identifying code 9.

The transmitting source identifying code 9 thus latched is supplied to avideo equipment body (not shown), and used in discriminating ordisplaying the signal transmitting source equipment. The transmittingsource identifying code 9 is supplied to the preceding transmittingsource identifying code holding circuit 4 and the transmitting sourceidentifying code comparator 5. The preceding transmitting sourceidentifying code holding circuit 4 is composed of a latch, for example.The preceding transmitting source identifying code holding circuit 4latches therein the one-field-preceding preceding transmitting sourceidentifying code 10, which was latched in the transmitting sourceidentifying code extracting circuit 3, in response to the transmittingsource identifying code latch pulse 25 supplied thereto as a clock.

The transmitting source identifying code comparator 5 compares thepreceding transmitting source identifying code 10 held in the precedingtransmitting source identifying code holding circuit 4 and thetransmitting source identifying code 9 thus newly latched by thetransmitting source identifying code extracting circuit 3. Therefore,when the transmitting source identifying code 9 and the precedingtransmitting source identifying code 10 are not agreed with each other,the transmitting source identifying code comparator 5 determines thatthe signal was switched, and then outputs the signal switching detectionsignal 11.

FIGS. 11A through 11I are timing charts showing a manner in which aswitching of a signal is detected at the field unit in the method of andapparatus for identifying a signal transmitting source according toanother embodiment of the present invention.

FIG. 11A shows the 10-bit parallel signal 6, FIG. 11B shows the headerdetection pulse 7, FIG. 11C shows the line number latch pulse 22, FIG.11D shows the transmitting source identifying code timing pulse 23, FIG.11E shows the line number signal 24, FIG. 11F shows the transmittingsource identifying code latch pulse 25, FIG. 11G shows the transmittingsource identifying code 9, FIG. 11H shows the preceding transmittingsource identifying code 10, and FIG. 11I shows the signal switchingdetection signal 11, respectively. A manner in which the switching ofsignal is detected will be described below.

As shown in FIG. 11A, the 10-bit parallel signal 6 is switched from asignal #1 to a signal #2 at a signal switching portion 71. A hatchedportion of the 10-bit parallel signal 6 represents the header of theSDDI format. The header is transmitted at every line. The 10-bitparallel signal 6 is supplied to the header detector 1, the line numberextracting circuit 20, and the transmitting source identifying codeextracting circuit 3 as shown in FIG. 9.

As shown in FIG. 11B, the header detector 1 generates the headerdetection pulse 7 by detecting the header of the SDDI format. The headerdetection pulse 7 is a pulse having a predetermined pulse width andwhich rises in synchronism with the leading edge of the header of theSDDI format. The header detection pulse 7 is outputted from the headerdetector 1 as shown in FIG. 9.

As shown in FIG. 11C, the timing generator 2 generates the line numberlatch pulse 22 on the basis of the header detection pulse 7 after apredetermined period of time from the header detection pulse 7. As shownin FIG. 9, the timing generator 2 outputs the line number latch pulse 22by counting the header detection pulse 7.

As shown in FIG. 11D, the timing generator 2 generates the transmittingsource identifying code timing pulse 23 on the basis of the headerdetection pulse 7 after a predetermined time from the header detectionpulse 7. As shown in FIG. 9, the timing generator 2 outputs thetransmitting source identifying code timing pulse 23 by counting theheader detection pulse 7.

As shown in FIG. 11E, the line number extracting circuit 20 generatesthe line number signal 24 whose one line ranges from the trailing edgeof the line number latch pulse 22 to the trailing edge of the next linenumber latch pulse 22. As shown in FIG. 9, the line number extractingcircuit 20 outputs the line number signal 24 by latching the 10-bitparallel signal 6 in response to the line number latch pulse 22 suppliedthereto as a clock.

As shown in FIG. 11F, only when the line number is the next line of thenext of the predetermined signal-switching positions 71, 72, i.e., linenumber 275 or line number 12, the line-masking circuit 21 opens its gateto pass the transmitting source identifying code timing pulse 23 to passtherethrough to provide the transmitting source identifying code latchpulse 25. As shown in FIG. 9, the line-masking circuit 21 outputs thetransmitting source identifying code latch pulse 25 by passing thetransmitting source identifying code timing pulse 23 therethrough onlywhen the line number signal is the line number 12 or 275.

As shown in FIG. 11G, the transmitting identifying code signal 9 ofaddress #2 is obtained at the trailing edge of the transmittingidentifying code latch pulse 25 that was first detected after the signalof the signal switching portion 71 has been switched. The addresses #1and #2 are addresses corresponding to the transmitting sources of thesignals #1 and #2.

As shown in FIG. 11H, there is obtained the one-field-precedingtransmitting source identifying code 10 of the transmitting sourceidentifying code 9. As shown in FIG. 9, the preceding transmittingsource identifying code holding circuit 4 outputs the precedingtransmitting source identifying code 10 by latching the transmittingsource identifying code 9 in response to the transmitting sourceidentifying code latch pulse 22 supplied thereto as a clock.

As shown in FIG. 11I, the signal switching detection signal 11 isobtained at the timing of the trailing edge of the transmitting sourceidentifying code latch pulse 25 that was first detected after the signalhas been switched. The signal switching detection signal 11 has aPredetermined time width corresponding to the difference of periodbetween the period of the transmitting source identifying code 9 and thepreceding transmitting source identifying code 10. As shown in FIG. 9,the transmitting source identifying code comparator 5 outputs the signalswitching detection signal 11 by comparing the transmitting sourceidentifying code 9 and the preceding transmitting source identifyingcode 10.

According to the above embodiment, the transmitting source identifyingcode is extracted from the SDDI format header of the received signal,the transmitting source identifying code indicative of the transmittingsource added to the transmission signal upon transmission is extracted,the change of the transmitting source identifying code indicative of thetransmitting source added to the transmission signal upon transmissionis detected, and the switching of the transmission signal is detectedbased on the transmitting source identifying code thus changed, therebymaking it possible to detect the switching of the transmitting source atthe field unit.

According to the above embodiment, since the transmitting sourceidentifying code 9 is provided in the header area 83 of the SDDI formatof the transmission signal, it is possible to detect the switching ofthe transmitting source identifying code 9 only by detecting the headerarea 83 of the SDDI format of the transmission signal.

According to the above embodiment, since the transmitting sourceidentifying code extracting circuit 3, the preceding transmitting sourceidentifying code holding circuit 4 and the transmitting sourceidentifying code comparing circuit 5 are provided at the front stage ofthe image information decoder 113, the audio information decoder 114 andthe control information decoder 115 for decoding the received signal,the image information decoder 113, the audio information decoder 114 andthe control information decoder 115 can effect various controloperations on image information, audio information and controlinformation based on the signal switching detection signal in thetransmitting source identifying code extracting circuit 3, the precedingtransmitting source identifying code holding circuit 4 and thetransmitting source identifying code comparator 5.

According to the above embodiment, the transmitting source identifyingcode change detecting means is the preceding transmitting sourceidentifying code holding circuit 4 for holding the precedingtransmitting source identifying code 10 which is one-frame-preceding orone-field-preceding the transmitting source identifying code 9 extractedby the transmitting source identifying code extracting circuit 3, andthe transmission signal switching detecting means is the transmittingsource identifying code comparator 5 for comparing the transmittingsource identifying code 9 extracted by the transmitting sourceidentifying code extracting circuit 3 and the preceding transmittingsource identifying code 10 held in the preceding transmitting sourceidentifying code holding circuit 4. With the above arrangement, thepreceding transmitting source identifying code 10 is held and thetransmitting source identifying code 9 and the preceding transmittingsource identifying code 10 are compared with each other, thereby makingit possible to detect the switching of the transmission signal.

According to the method of identifying a transmitting source wherein thetransmitting source identifying code 9 is added to the transmissionsignal at the transmission end of the transmission line, thetransmitting source identifying code 9 is extracted from the receivingend of the transmission line, the change of the transmitting sourceidentifying code 9 extracted at the receiving end is changed and theswitching of the transmission signal is detected on the basis of thechanged transmitting source identifying code 9, it is possible to detectthe switching of the transmission signal.

When image information is compressed and encoded, it is frequentlyobserved that image information is compressed by use of interfield orinterframe correlation. At that time, the image information is encodedover a plurality of fields. As a result, if this image information isswitched in somewhere of the image information, then a reproducedpicture is destroyed at the succeeding field. Therefore, when imageinformation is compressed and encoded, in order to initialize an imagereproducing circuit, the compression and encoding of image informationmay be completed at a constant period, e.g., 2 frames, for example. Withthe above arrangement, even when the circuit is activated or compressedand encoded data is destroyed due to some cause, a normal reproducedimage can be obtained after the period in which the encoding iscompleted.

The image information decoder 113 discards reproduced images obtainedafter the field where the switching of signal was detected and continuesoutputting reproduced images obtained immediately before the switchingwhen a switching of signal is detected during compressed and decodedimage information is received (when the image information decoder 113 issupplied with the signal switching detection signal 11 or 118). Withthis arrangement, a destroyed reproduced image can be prevented frombeing outputted, and a so-called freeze picture can be outputted. Then,if a normal reproduced image is outputted from the next code completionperiod, then it is possible to prevent a reproduced image from beingdestroyed when the signal is switched.

When audio information is compressed and encoded, it is frequentlyobserved that audio information is compressed by use of correlation ofpreceding and succeeding samples. At that time, audio information isencoded over a plurality of fields. If such audio information isswitched in somewhere of the audio information, then a reproduced soundis destroyed at the succeeding samples. When audio information iscompressed and encoded, in order to initialize an audio reproducingcircuit, a compressed code may be completed at a constant period, e.g.,2 frames. With such arrangement, even if compressed and encoded audiodata is destroyed when the circuit is activated or due to some cause, anormal reproduced sound can be obtained after the period wherein thecompressed code has been completed.

When the audio information decoder 114 detects the switching of signalduring compressed and encoded audio information is received (when thesignal switching detection signal 11 or 118 is supplied to the audioinformation decoder 114), a reproduced sound obtained after the samewherein the switching was detected is muted. With the above arrangement,destroyed reproduced sound can be prevented from being outputted. Ifnormal reproduced sound is outputted after the period wherein thecompressed code has been completed, then it is possible to preventreproduced sound from being destroyed due to the switching of signal.

Further, if data of control signal is switched in somewhere of data,then a received control signal becomes erroneous. If such erroneouscontrol signal is used as it is, then the system will malfunction.Accordingly, when the control information receiver 115 detects theswitching of signal during control information is received (when thesignal switching detection signal 11 or 118 is supplied to the controlinformation receiver 115), the control information receiver 115 discardsreceived control information, and holds the previous state. With theabove arrangement, it is possible to prevent the system frommalfunctioning.

While the system of the SDDI format in the synchronization of 525/60system has been described so far, the principle of the present inventioncan be similarly applied to the system of SDDI format of othersynchronization such as the 625/50 system.

Further, while the data transmission using the coaxial cable has beendescribed so far, the principle of the present invention can besimilarly applied to other transmission systems, such as optical fibertransmission system or radio communication system.

As described above, the transmitting source identifying code has alreadybeen standardized as the format in the header of the SDDI format. Thetransmission and reception system according to the SDDI format that hasbeen previously-proposed by the same assignee of the present applicationis provided with both a transmitting source identifying code addingcircuit on the transmission side (not shown) and the transmitting sourceidentifying code extracting circuit 3 on the reception side. Therefore,without adding new information on the transmission side and withoutadding a new circuit on the transmission side, a switching of signal canbe detected with a high reliability by addition of a simplifiedcomparing circuit on the reception side.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

What is claimed is:
 1. A digital data transmission apparatus comprising:digital packet generating means for generating a first digital packetconforming to the format for a second digital packet standard, saidfirst digital packet comprising: a payload portion into which digitaldata is inserted; a first start synchronization code storage portionpositioned at a preceding portion of said payload portion into which astart synchronization code is inserted, said start synchronization codeindicating a start of said digital data inserted into said payloadportion; a first end synchronization code storage portion into which anend synchronization code is inserted, said end synchronization codeindicating an end of said digital data inserted into said payloadportion; and an ancillary data storage portion positioned between saidfirst end synchronization code storage portion and said first startsynchronization code storage portion, and into which an ancillary dataincluding an error detection code for detecting a line number error isinserted; wherein said second digital packet comprises: an active videoportion corresponding to said payload portion into which video data isinserted; a second start synchronization code storage portioncorresponding to said first start synchronization code storage portionpositioned at a preceding portion of said active video portion intowhich said start synchronization code is inserted, said startsynchronization code indicating a start of said video data inserted intosaid active video portion; a second end synchronization code storageportion corresponding to said first end synchronization code storageportion into which said end synchronization code is inserted, said endsynchronization code indicating an end of said video data inserted intosaid active video portion; and an auxiliary data storage portioncorresponding to said ancillary data storage portion positioned betweensaid second end synchronization code storage portion and said secondstart synchronization code storage portion, and into which auxiliarydata is inserted; said error detection code for detecting a line numbererror is inserted in said first digital packet at an error detectioncode storage portion positioned immediately after a line number storageportion into which data indicating said line number is inserted in saidancillary data storage portion, said line number portion beingpositioned in proximity to said first end synchronization code storageportion; and serial data transmitting means for converting said firstdigital packet into serial digital data, and for transmitting saidserial digital data.
 2. The digital data transmitting apparatusaccording to claim 1, wherein said error detection code is CRC code. 3.The digital data transmitting apparatus according to claim 1, whereinsaid digital data inserted in said payload portion is data includingcompressed video data.
 4. The digital data transmitting apparatusaccording to claim 1, wherein said format for said first digital packetis defined by SMPTE-259M.
 5. A digital data transmission method,comprising the steps of: generating a first digital packet conforming tothe format for a second digital packet standard, said first digitalpacket comprising: a payload portion into which digital data isinserted; a first start synchronization code storage portion positionedat a preceding portion of said payload portion into which a startsynchronization code is inserted, said start synchronization codeindicating a start of said digital data inserted into said payloadportion; a first end synchronization code storage portion into which anend synchronization code is inserted, said end synchronization codeindicating an end of said digital data inserted into said payloadportion; and an ancillary data storage portion positioned between saidfirst end synchronization code storage portion and said first startsynchronization code storage portion, and into which an ancillary dataincluding an error detection code for detecting a line number error isinserted; wherein said second digital packet comprises: an active videoportion corresponding to said payload portion into which video data isinserted; a second start synchronization code storage portioncorresponding to said first start synchronization code storage portionpositioned at a preceding portion of said active video portion intowhich said start synchronization code is inserted, said startsynchronization code indicating a start of said video data inserted intosaid active video portion; a second end synchronization code storageportion corresponding to said first end synchronization code storageportion into which said end synchronization code is inserted, said endsynchronization code indicating an end of said video data inserted intosaid active video portion; and an auxiliary data storage portioncorresponding to said ancillary data storage portion positioned betweensaid second end synchronization code storage portion and said secondstart synchronization code storage portion, and into which auxiliarydata is inserted; said error detection code for detecting a line numbererror is inserted in said first digital packet at an error detectioncode storage portion positioned immediately after a line number storageportion into which data indicating said line number is inserted in saidancillary data storage portion, said line number portion beingpositioned in proximity to said first end synchronization code storageportion; converting said first digital packet into serial digital data;and transmitting said serial digital data.
 6. The digital datatransmitting method according to claim 5, wherein said error detectioncode is CRC code.
 7. The digital transmitting method according to claim5, wherein said digital data inserted in said payload portion is dataincluding compressed video data.
 8. The digital data transmitting methodaccording to claim 5, wherein said format for said first digital packetis defined by SMPTE-259M.
 9. A digital data transmission signalcomprising: a first digital packet conforming to the format for a seconddigital packet standard, said first digital packet comprising: a payloadportion into which digital data is inserted; a first startsynchronization code storage portion positioned at a preceding portionof said payload portion into which a start synchronization code isinserted, said start synchronization code indicating a start of saiddigital data inserted into said payload portion; a first endsynchronization code storage portion into which an end synchronizationcode is inserted, said end synchronization code indicating an end ofsaid digital data inserted into said payload portion; and an ancillarydata storage portion positioned between said first end synchronizationcode storage portion and said first start synchronization code storageportion, and into which an ancillary data including an error detectioncode for detecting a line number error is inserted; wherein said seconddigital packet comprises: an active video portion corresponding to saidpayload portion into which video data is inserted; a second startsynchronization code storage portion corresponding to said first startsynchronization code storage portion positioned at a preceding portionof said active video portion into which said start synchronization codeis inserted, said start synchronization code indicating a start of saidvideo data inserted into said active video portion; a second endsynchronization code storage portion corresponding to said first endsynchronization code storage portion into which said end synchronizationcode is inserted, said end synchronization code indicating an end ofsaid video data inserted into said active video portion; and anauxiliary data storage portion corresponding to said ancillary datastorage portion positioned between said second end synchronization codestorage portion and said second start synchronization code storageportion, arid into which auxiliary data including said error detectioncode is inserted; said error detection code for detecting a line numbererror is inserted in said second digital packet at an error detectioncode storage portion positioned immediately after a line number storageportion into which data indicating said line number is inserted in saidancillary data storage portion, said line number portion beingpositioned in proximity to said first end synchronization code storageportion; wherein said first digital packet is converted into serialdigital data and is transmitted, and at least said stored ancillary datais used to direct the operation of a playback device.
 10. The digitaldata transmission signal according to claim 9, wherein said errordetection code is CRC code.
 11. The digital transmission signalaccording to claim 9, wherein said digital data inserted in said payloadportion is data including compressed video data.
 12. The digital datatransmission signal according to claim 9, wherein said format for saidfirst digital packet is defined by SMPTE-259M.